The invention relates to a multipole current-limiting circuit breaker with molded insulating case, housing:
a current interrupting device having per pole contact elements separable by electrodynamic repulsion, and at least one arc extinguishing chamber,
an operating mechanism having a toggle associated with a connecting spring, and with a trip device,
a switching bar made of insulating material acting as support for the movable contacts of all the poles, said bar being mechanically coupled to the toggle to be moved by the mechanism between the closed position and the open position of the contacts,
a handle coupled to the mechanism and passing through an aperture in the front panel of the case,
the movable contact of each pole being formed by a contact arm articulated on a spindle securedly united to the bar, said movable contact being able to be moved by electrodynamic repulsion from a first rest position to a second active position, and the spindle of the movable contact being eccentric with respect to the rotation axis of the bar,
and flexible means comprising a spring housed in a recess of the bar to provide the contact pressure and to slow down the drop-back of the movable contact to the first rest position, the spring sliding on a bearing surface of the movable contact to modify the application point of the pressure force P in the course of the opening travel.
In this first type of current-limiting circuit breaker, the occurrence of a short-circuit causes in a first phase high-speed opening, by electrodynamic repulsion, of the contacts of the faulty pole, and in a second phase tripping of the mechanism controlled by the tripping means. Rotation of the switching bar for final opening of the contacts takes place only during the second phase after the trip lever has been unlocked by the latch.
The arm remains immobile during the first electrodynamic repulsion phase.
Only the contact arm of the faulty pole opens, the contacts of the other poles remaining closed during this first phase. It is essential that rotation of the bar for confirmation of opening of the circuit breaker take place before the contact arm drops back to the closed position. The coordination defect between the two phases is mainly due to the bar being held in the closed position during the first repulsion phase and may cause contact chatter and premature wear of the circuit breaker.
According to U.S. Pat. No. 4,480,242, the movable contact is subjected to a variation of the contact pressure spring restoring torque, said torque being increasing up to an intermediate position of the opening travel, then decreasing up to the open position.
The document FR-A-2,553,930 filed by the applicant belongs to a second type of current-limiting circuit breaker having a reversible mechanism, in which the rotation spindle of the bar coincides with the articulation point of each contact arm. The drag spring is anchored between the movable contact and the bar.
The contact arm of each pole cooperates with the toggle device to drive the switching bar in rotation in the opening direction after the electrodynamic repulsion means of the faulty pole have come into action so as to enable separation of the contacts of all the poles before the trip lever is unlocked by the latch.
The reversibility of the mechanism by rotation of the bar during the first electrodynamic opening phase speeds up the tripping time to confirm final opening of the circuit breaker. Rotation of the bar before operation of the trip device is rendered possible due to the deformation of the toggle, the rods there having an offset angle between 10 and 20 degrees on the closed position.